1. Field of the Invention
The present invention relates to an inkjet recording apparatus and method, and an abnormal nozzle detection method, and in particular to technology for detecting ejection defects (flight deviation of ejected droplets, volume abnormality of ejected droplets, splashing, ejection failure, and the like) occurring in an inkjet head having a plurality of nozzles (droplet ejection ports), and to correction technology for suppressing decline in image quality arising from nozzles having abnormalities.
2. Description of the Related Art
An inkjet apparatus forms images by ejecting and depositing a functional material (hereinafter, taken to be synonymous with “ink”) using an inkjet head, and has characteristic features which include: excellent eco-friendly properties, capability for high-speed recording on various different recording media, the capability to achieve high-definition images which are not liable to bleeding.
However, in recording by an inkjet method, ejection defects occur with a certain probability in nozzles of the inkjet head, and stripe non-uniformities and density non-uniformities occur in recorded images at positions corresponding to the defective nozzles. These ejection defects which lead to decline in image quality produce an increase in wasted paper and give rise to a decline in throughput due to the carrying out of head maintenance.
In particular, in a single-pass method which performs image formation by means of one recording scan, even an ejection defect in one nozzle has a great effect on the overall image quality. Moreover, in the case of a single-pass method which emphasizes productivity, since the inkjet head is always positioned above recording media, then it is difficult to carry out head maintenance during the image formation operation.
Possible causes of the occurrence of ejection defects in the inkjet heads include: decline in ejection force due to bubbles which have entered into the nozzles, adherence of foreign matter to the vicinity of the nozzles, abnormality in the liquid-repelling properties in the vicinity of the nozzles, abnormality in the nozzle shapes, and the like. Moreover, a nozzle that has produced an ejection defect is liable to create an ink mist due to instable ejection, and this mist causes deterioration of the surrounding nozzles which are normally functioning. Various countermeasures have been proposed for suppressing the occurrence of ejection defects, such as deaeration of the ink (Japanese Patent Application Publication No. 05-017712), suctioning of ink mist (Japanese Patent Application Publication No. 2005-205766), and the like. However, it is difficult to completely prevent ejection defects.
In response to these problems, a method which detects, in advance, nozzles that are likely to produce ejection defects has been proposed (Japanese Patent Application Publication Nos. 2003-205623 and 11-348246).
Japanese Patent Application Publication No. 2003-205623 discloses technology for performing ejection failure nozzle detection at a maintenance position outside an image formation region by using a waveform that is different from a recording waveform, and carrying out maintenance in cases where an ejection failure has been detected. However, this technology has a problem in that throughput declines due to adopting a composition in which the print head is moved to the maintenance position outside the image formation region, and the ejection failure nozzle detection and the maintenance are carried out at the maintenance position. Moreover, it is silent about detection of ejection defects (e.g., flight deviation and splashing) other than ejection failures, and the actual waveform used for detection is not made clear.
Japanese Patent Application Publication No. 11-348246 discloses technology for detecting nozzles which have ejection abnormally and performing correction by means of the surrounding nozzles which are operating normally. However, in order to detect perceivable ejection abnormalities, the technology requires an expensive detective device, such as a high-resolution imaging device (e.g., CCD) capable of accurately determining the deposition of ink droplets or a device capable of measuring the state of flight of ink droplets, or the like; it also takes time for the detection process. Moreover, since it is not possible to detect abnormalities during image formation with this technology, then throughput declines.
As stated above, it has been difficult to achieve both recording stability and throughput in the related art.